docs: def segments_overlapping(ab, cd):
      '''
      segments_overlapping((a, b), (c, d)) yields True if the line segments (a,b) and (c,d) are both
      colinear and have a non-finite overlap. If (a,b) and (c,d) touch at a single point, they are not
      considered overlapping.
      '''
      (a,b) = ab
      (c,d) = cd
      ss = [point_in_segment(ab, c), point_in_segment(ab, d),
            point_in_segment(cd, a), point_in_segment(cd, b)]
      return (~(points_close(a,b) | points_close(c,d)) & 
              ((np.sum(ss, axis=0) > 1) |
               (points_close(a,c) & points_close(b,d)) |
               (points_close(a,d) & points_close(b,c))))